Observer pattern is not working in Android MVVM - kotlin

Question

I am trying to update my view according to my data in my ViewModel, using MVVM
I need in the method onCacheReception to update my map whenever zones is changing
ViewModel
class MainViewModel constructor(application: Application) : AndroidViewModel(application),
CacheListener {
private val instance = Initializer.getInstance(application.applicationContext)
private val _zones = MutableLiveData<List<Zone>>()
val zones: LiveData<List<Zone>>
get() = _zones
init {
CacheDispatcher.addCacheListener(this)
}
override fun onCacheReception() {
val zonesFromDB: List<Zone>? = instance.fetchZonesInDatabase()
_zones.value = zonesFromDB
}
}
MainActivity
class MainActivity : AppCompatActivity(), EasyPermissions.PermissionCallbacks, OnMapReadyCallback {
private val mainViewModel: MainViewModel = ViewModelProvider(this).get(MainViewModel(application)::class.java)
private lateinit var initializer: Initializer
private lateinit var map: GoogleMap
private val REQUEST_CODE_LOCATIONS: Int = 100
private val permissionLocationsRationale: String = "Permissions for Fine & Coarse Locations"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
if (checkForLocationsPermission()) {
setUp()
mapSetUp()
}
mainViewModel.zones.observe(this, Observer { zones ->
zones.forEach {
Log.i("YES DATA", "Data has been updated")
val latLng = it.lat?.let { it1 -> it.lng?.let { it2 -> LatLng(it1, it2) } }
val markerOptions = latLng?.let { it1 -> MarkerOptions().position(it1) }
map.addMarker(markerOptions)
}
})
}
My Log is never displaying and it doesn't seem while debugging that mainView.zones.observe { } is called when I receive some new data in my ViewModel

Answer 1

In the onCacheReception(), replace:
_zones.value = zonesFromDB
by:
_zones.postValue(zonesFromDB)
in case your onCacheReception() function is called from a worker thread.